So Gilbert, Faculty Director of the Microbiome Center, and Rob Knight, PhD, Director of the Center for Microbiome Innovation at the University of California, San Diego, teamed up to provide some answers in their new book, "Dirt is Good: The Advantage of Germs for Your Child's Developing Immune System" (St. Martin's Press, $25.99). The book is an accessible guide to the role of the microbiome - the tiny organisms in, on and around our bodies - in health and well-being. In the introduction, the authors write that their goal is "to present you, too, with the best scientific advice available about the microbiome and your children's health and development."